Effect of inhibition of _IIbβ₃ engagement on thrombin-induced JNK1 activation. Washed platelets were preincubated at 37°C for 30 seconds in the presence or absence of peptides RGDS and RGES (0.5 mmol/L and 1 mmol/L) (A) or with various concentrations of the (Fab′)₂ fragment of the anti-_IIbβ₃ monoclonal antibody AP-2 (0 to 20 μg/mL) for 5 minutes (B). They were then incubated with 0.2 U/mL with stirring for 2 minutes. JNK1 phosphorylation was studied by Western blotting and JNK1 activity by phosphorylation of GST-cJun, as described in Fig 1. Autoradiographs were scanned with a laser densitometer. For each experiment, the ratio of JNK1-P or GST-cJun was normalized to that of platelets treated with thrombin alone and is expressed as a relative intensity. Results are the means ± SEM for four experiments.